The influence of microstructure on the mechanical properties of polycrystalline diamond: a literature review

Abstract

Polycrystalline diamond (PCD) is an extremely high-performance cutting tool material used in the machining of rock, high-strength, non-ferrous metal alloys and carbon-fibre-reinforced composites. It is favoured for its exceptional hardness and wear resistance which results in at least an order of magnitude improvement in performance over previous technologies in almost all metrics. However, PCD suffers from unpredictable brittle fracture and degradation at high temperature during service which limits its capabilities in cutting applications. The literature on the link between its microstructure and its mechanical properties, including strength, toughness and flaw size distribution as measured by pseudo-static tests, is investigated. The conclusions of the seminal paper on this topic are re-examined in the light of modern ceramics research and an alternative explanation is put forth for the strengthgrain size relationship published in this paper. All known literature values for strength and toughness vs. grain size and binder content are collated showing no overall trend in strength with binder content but moderate trends in all other combinations. The common claim of weak grain boundaries is brought into question in the light of the lack of any evidence of this fracture mode being evident in pseudo-static tests. The industrial literature on wear testing and failure modes of PCD in service and service-like tests is examined to bridge the gap between pseudo-static and dynamic, application-based experiments. Six main failure modes are recorded and summarised with intergranular fracture being the most conspicuously absent from the pseudo-static tests. It is suggested that the temperature generated by friction in dynamic tests causes the weakening of grain boundaries, resulting in a transition from transgranular to intergranular fracture and a call for further research in this area is made.

Microhardness and wear behaviour of polycrystalline diamond after warm laser shock processing with and without coating

“…The use of synthetic polycrystalline diamond (PCD) in construction, subterranean mining and oil and gas drilling applications has increased throughout the years since first invented in 1960s, due to the highly desirable characteristics offered by this material over monocrystalline diamond [1], [2]. PCD consists of several randomly arranged single crystals or grains that are separated by regions called grain boundaries, producing a composite structure with isotropic properties [3].…”

“…Despite the advantages of PCD over monocrystalline diamond and other conventional materials used for cutting tools, PCD are exposed to high temperatures and complex wear environments (which are known to cause impact and fretting fatigue) in oil and gas and mining applications, and they can fail due to one or a combination of the following failure modes: smooth wear, gross and micro-chipping, spalling, and gross fracturing. Hence, it is essential that they have exceptional wear/abrasion resistance, impact resistance, fracture toughness and thermal stability [2], [7]. These properties are a result of the microstructural characteristics of PCD materials [2], thus by designing the microstructural characteristics (e.g.…”

“…Hence, it is essential that they have exceptional wear/abrasion resistance, impact resistance, fracture toughness and thermal stability [2], [7]. These properties are a result of the microstructural characteristics of PCD materials [2], thus by designing the microstructural characteristics (e.g. diamond grain size and binder volume) it is possible to enhance the performance for a specific application.…”

“…The effect of LPwC on wear, friction characteristics and micro hardness properties of PCD has never been investigated before. In the need of improving PCDs' resistance to impact and shock loading [2] and enhancing PCDs' wear performance in real machining applications, the objectives of the proposed research are twofold. Firstly, two laser processing methods are proposed to improve wear resistance and micro-hardness of polycrystalline diamond composites while maintaining finishing tolerances.…”

Applications of Diamond to Improve Tribological Performance in the Oil and Gas Industry

“…In many examples where diamond found application in the oil and gas industry, it was in the form of polycrystalline diamond (PCD), which is produced by sintering diamond grains on a cemented tungsten carbide (WC) substrate at high pressure. Presses typically apply 4-10 GPa of pressure at temperatures of between 1400 and 1800 • C [3]. Under these conditions, molten cobalt (Co), which is present as the binder phase in the substrate, infiltrates the pores between the diamond grains to facilitate the sintering process.…”